Email Signature with Logo

Email Signature with Logo

Is there a way to call an logo file from a server in our signatures?  My clients tell me that my signature shows up as an attachment instead of pulling it from a server.  I tried to add the signature log in the settings and it displays correctly but goes to the cleint as an attachment.  I also tried to add HTML in that portion like <img src="www.server.com/email_logo.jpg"> (example) and that wont work either.